This invention relates generally to injection molding machines and more particularly to an aligning device for a table used on injection molding machines having vertically oriented clamp systems.
xe2x80x9cVerticalxe2x80x9d injection molding machines consist of an injection unit mounted either with a horizontal or vertical orientation and a clamp system oriented vertically to hold the two mold halves together under force sufficient to resist the pressure exerted by the molten plastic. Orientation of the clamp system vertically allows for operational ease as compared with horizontal clamp systems for certain applications including, but not limited to, insert molding and cable connectors.
Vertical injection molding machines can be equipped with a rotating table mounted to rest on the stationary platen. A plurality of lower mold halves are mounted on the table at set positions or stations. The table rotates a set amount to bring a lower mold half into alignment with an upper mold half mounted on the vertically movable platen. The upper mold half mates with the lower mold half, molding material is injected, packed, and the movable platen withdrawn upward. The lower mold half with the molded part therein is now indexed or rotated to another station. At the same time, a xe2x80x9cfreshxe2x80x9d lower mold half also mounted to the table and previously positioned at some station on the table where it is made ready for molding, is rotated into molding relationship with the upper mold half.
At least two stations are provided in the rotating table, i.e., an injection station and an ejection station. By performing ejection away from the injection station, it may be possible for certain molding applications to reduce cycle time as contrasted to the traditional horizontal injection molding machine which must eject the molded part from the mold cavity. While time is spent indexing the part, that time can be spent in cooling the part which must occur no matter which machine is used before ejection can happen. Usually, the table is equipped with two, three or more stations and the additional stations typically involve stations that set inserts. Thus, a three station table will typically have a separate insert station which occurs after ejection and prior to injection.
All stations are typically automated. At the ejector station, ejector pins, typically positioned beneath the table, dislodge the molded part from the lower mold half and a robotic arm typically transfers the part from mold half to some other station in the plant. Similarly, robotic arms subsequently set inserts into the now empty lower mold half at the insert station. Because of the vertical positioning of the lower mold half with exposed upward cavity, there is an orientation advantage enjoyed by the vertical injection molding machine making it receptive to molding parts requiring a number of intricately placed inserts.
It is to be appreciated that the vertically oriented clamp system with stationary platen fixed to ground lends itself well to high tonnage moldings having relatively heavy mold halves. In addition, advances in molding technology have improved the quality of molded parts produced today and require that the mold halves be precisely aligned. Alignment is conventionally assured by guide pins from one of the mold halves received in guide pin holes in the other mold half. Tolerances between guide pins and guide pin holes are therefore reduced to assure precise alignment of the mating mold halves required (among other things) for precision molding. At the same time, heavy mold parts in a vertical injection mold machine can excessively wear the guide pins if the bottom mold half is not rotated into accurate alignment with the upper, vertically movable mold half.
The problem to which the invention is directed may best be understood by reference to the schematic prior art arrangement depicted in FIG. 1. FIG. 1 shows an upper mold half 1 with guide pins 2 which will vertically descend into mating relationship with a lower mold half 3 mounted on rotatable table 4 by guide pins 2 nesting into guide pin holes 5. Table 4 is also shown in top view between the vertically displaced upper mold half 2 and lower mold half 3. In the top view, the lower mold half at the injection station is designated 3A, at the ejection station 3B, and at the insert station 3C.
Typically, table 4 is rotated about its center by a drive (not shown). A limit or proximity switch is manually set to be actuated when the table rotates to its next successive position. That is when lower mold half 3C rotates to the injection station (shown occupied by lower mold half 3A in FIG. 1), the switch is actuated and the drive stops. For a number of reasons, the switch cannot precisely position the lower mold half at the injection station to assure alignment of guide pins 2.
The prior art has recognized this and has provided an aligning mechanism for the table. This aligning mechanism conceptually comprises a locating hole 6 in table 4 and a power driven locating pin 7. Specifically, one power driven locating pin 7 is provided and table 4 has at each station a locating hole designated 6A, 6B, and 6C in the plan view. When the switch is actuated to stop table rotation, final alignment results by the tapered locating pin 7 fitting into locating hole 6. This causes a slight rotational movement of table 4 and brings lower mold half 3 into better alignment with upper mold half 1 as locating pin 7 is forced upwardly into locating hole 6 than the alignment possible using only a manually set switch. The system described works and has produced acceptable molded parts for years.
For precision molding with good guide pin life, the prior art system is not acceptable. Table 4 is a large diameter and sophisticated jigs and fixtures are used to drill locating holes 6. Size of locating holes 6 and, more importantly, position of locating holes 6, can be held to tolerances of xc2x10.003xe2x80x3. The cumulative effect of hole tolerance in the table can account for 0.010xe2x80x3 to 0.012xe2x80x3 variation in hole position which is not acceptable. It is to be also recognized that there are variations in other manufacturing tolerances that also contribute to random positioning of the locating holes in the table. For example, variations in the spindle (about which the table rotates) and variations in the gear drive arrangement also account for variations in the position of the locating holes in the table. The cumulative effect of all the tolerances, as well as slippage in the drives, reduce the diametrical size of the locating pin to a dimension not acceptable for the heavy mold, high precision moldings desired to be produced for certain molding applications.
The effect of positional variation in the locating holes is illustrated diagrammatically in exaggerated form by the overlay of locating holes 6A, 6B, 6C shown in the upper right hand corner of FIG. 1. Assume table 4 can be stopped at a precise rotational angle so that no variation in rotation occurs when the table is indexed. Locating hole 6A will occupy the position shown by the solid circle, locating hole 6B will occupy the position shown by the dash circle and locating hole 6C will occupy the position shown by the dot-dash circle. Common area for all three locating holes is shown by cross-hatching and is a reduction in the effective size of locating hole 6. This means that the locating pin can only be the diameter of the reduced locating hole size if the locating pin is to extend through all three locating holes. Reducing the diameter of the locating pin, even in the range of 0.01041, will not provide the desired accurate positioning of the lower mold half relative to the upper, vertically movable mold half.
Accordingly, it is an object of the invention to overcome the alignment problem discussed above resulting in a reduction of guide pin wear and/or precision molding for certain molding applications.
This object along with other features of the invention is achieved in a vertical injection molding machine which has a lower stationary platen, an upper vertically movable platen with an upper mold half mounted thereon and a table rotatably mounted on the stationary platen and having a plurality of lower mold half stations circumferentially spaced thereabout. Each lower mold half station has a plurality of mounting apertures for variably mounting a lower mold half in each station and the machine is equipped with a drive mechanism for rotating a table from one station to another. An improved aligning mechanism is provided for assuring that the table has stopped at a position whereat the upper and lower mold halves have guide pins and guide pin holes in alignment with one another.
The aligning mechanism includes a locating hole in the table at each station and a locating pin having a tapered tip and a tubular body with a peripheral configuration of size and shape sufficient to establish a slip fit with the locating hole. An actuator is secured to the locating pin for moving the locating pin from an initial position whereat the tapered tip does not extend into the table (preferably from a position below the table) to a located position whereat the body of the locating pin is within the locating hole. Importantly, a guide rail is secured to one of the actuator and the stationary platen and a runner block slidable in the guide rail is mounted to the other one of the actuator and stationary platen whereby movement of the tapered tip into the locating hole by the actuator from the initial position causes movement of the table in a rotating direction and movement of the locating pin in the direction of the guide rail to assure seating of the body of the locating pin into the locating hole notwithstanding variations in manufacturing tolerances as well as other variations causing positional changes of the locating holes from their designed position.
In accordance with a specific aspect of the invention, the locating hole and the pin body are cylindrical and the sliding fit is established as a space between pin body and locating hole not exceeding about 0.002xe2x80x3 for any locating hole position.
In accordance with another specific but important aspect of the invention, the rail is preferably straight and oriented at any direction which intersects a radial arc drawn from the center of the table and passing through a locating hole thereby assuring that the center of the pin will coincide with the center of the locating hole by slight rotational table movement caused by the pin entering the hole coupled with linear motion of the runner block within the guide rail.
In accordance with a more specific aspect of the invention, the arrangement includes a mounting block through which the locating pin extends. The mounting block is secured to the actuator at one end thereof and the runner block is secured to a side of the mounting block while the rail isl secured to the stationary platen. A stopper bracket is provided and mounted to the platen adjacent the rail. The stopper bracket has a stop slot extending in the direction of the rail and a stop pin secured to the end of the runner block extends into the stop slot for limiting travel of the runner block in a simple mounting arrangement which can be readily attached to a flat face surface of the stationary platen. Alternatively, the rail is secured to the mounting block and the runner block is secured to the stationary, lower platen.
In general summary, inventive objects, features and advantages of the present invention relate to an aligning mechanism for a vertical injection molding machine equipped with a rotating table which has one or more, or any combination, of the following characteristics or attributes:
a) minimize mold half guide pin wear;
b) enhance precision molding characteristics of the vertical machine;
c) enhance the ability of the vertical machine to accurately mold parts in cavities of large and/or heavy mold halves;
d) suitable for application with heavy rotating tables that must be lifted while rotatably indexed; and/or
e) an especially simple and effective mounting arrangement for the locating pin actuator which can be implemented in a cost efficient manner without extensive machining of parts and assembly.